ibft: Update iBFT handling for v1.03 of the spec.

- Use struct acpi_table_ibft instead of struct ibft_table_header
- Don't do reserve_ibft_region() on UEFI machines (section 1.4.3.1)
- If ibft_addr isn't initialized when ibft_init() is called, check for
  ACPI-based tables.
- Fix compiler error when CONFIG_ACPI is not defined.

Signed-off-by: Konrad Rzeszutek Wilk <konrad@kernel.org>
Signed-off-by: Peter Jones <pjones@redhat.com>
Signed-off-by: Mike Christie <michaelc@cs.wisc.edu>